Hello, I’m having the same issue. I moved my reverse proxy on unraid from SWAG (which had no certificate problem) to Nginx Proxy Manager. I am using Lets Encrypt for my domain nextcloud.server.com and it works great on all browsers, but not the desktop apps. I get the same error you mentioned. I have never messed with certificates. I do not know where to find them to delete the old one. I’m using unraid 6.9.2 for my nextcloud. Any advice or directions would be appreciated. Thanks